AUGUSTA — A key witness in a recent high-profile arson trial was hospitalized Thursday after he reportedly attempted to strangle himself inside a cell at the Kennebec County jail.

Thomas J. Mulkern, 26, of Gardiner, was arrested Tuesday in Waterville after police there charged with him stealing from an apartment and chased after him. Mulkern, jailed after the Waterville incident, was taken to MaineGeneral Medical Center Thursday after he tried to strangle himself with a twisted bed sheet, said Kennebec County Sheriff Randall Liberty.

“He was responding and alert and talking,” Liberty said.

Mulkern was expected to return to the jail Thursday night. Liberty said Mulkern will be placed on watch, which includes a check every five minutes.

Waterville police arrested Mulkern, who was wearing blue hospital scrubs, and charged him with theft, refusing to submit to detention and a probation hold after officers responded to a report of stolen money from a house on High Street. The previous night Mulkern had been taken to the hospital on suspicion that he was under the influence of the drug known as bath salts, police said.

Mulkern struggled with police and had to be subdued with a Taser, Waterville Police Deputy Chief Charles Rumsey said after the arrest.

Mulkern was taken to the Kennebec County jail following the Waterville incident. Mulkern on Wednesday became aggressive with corrections officers, who used pepper spray to bring him under control, Liberty said.

“He became difficult,” Liberty said. “He saw his girlfriend in the jail and he wanted to talk to her. That caused the conflict.”

Mulkern was placed in an observation cell Wednesday night. Around 11 a.m., officers checked on him and found him unconscious with the sheet around his neck, Liberty said.

Mulkern provided key testimony late last month in Raymond Bellavance Jr’s arson trial in Kennebec County Superior Court. A jury on Dec. 30 convicted Bellavance of burning down the Grand View Topless Coffee Shop in Vassalboro.

Mulkern testified that he accompanied Bellavance and watched him set the building on fire with gas cans. Saying he wanted to clear his conscience after recently completing a drug rehabilitation program in jail, Mulkern reversed his previous story that he was elsewhere when the fire was set.

In exchange for his unexpected testimony, Mulkern was given immunity from prosecution for any charges related to the coffee shop fire, including illegal drug use.

Liberty said that Mulkern recently graduated from the Kennebec County’s Criminogenic Addiction Recovery Academy, which is designed to treat those whose criminal activity is fueled by their substance abuse.

“He struggles with substance abuse and mental health,” Liberty said. “We had high hopes for him.”

Craig Crosby — 621-5642

ccrosby@centralmaine.com